HALO DENSITY REDUCTION BY BARYONIC SETTLING?

We test the proposal by El-Zant et al. that the dark matter density of halos could be reduced through dynamical friction acting on heavy baryonic clumps in the early stages of galaxy formation. Using N-body simulations, we confirm that the inner halo density cusp is flattened to 0.2 of the halo break radius by the settling of a single clump of mass greater than or similar to 0.5% of the halo mass. We also find that an ensemble of 50 clumps, each having masses greater than or similar to 0.2%, can flatten the cusp to almost the halo break radius on a timescale of similar to 9 Gyr, for a Navarro-Frenk-White profile halo of concentration 15. We summarize some of the difficulties that need to be overcome if this mechanism is to resolve the apparent conflict between the observed inner densities of galaxy halos and the predictions of.CDM.